PREVALENCE AND PHENOTYPES OF CONGENITAL MYOPATHY DUE TO α-ACTIN 1 GENE MUTATIONS

Introduction: Congenital myopathy due to mutations in the a-actin 1 gene (ACTA1) was identified in 1999, but knowledge of prevalence and phenotype in patients who survive 5 years is lacking. Methods: A national cohort of 91 patients aged >= 5 years and diagnosed with congenital myopathy was assessed for ACTA1 mutations and investigated clinically. Results: Four patients with ACTA1 mutations were identified, yielding a prevalence of 4.4%. Patients were 10-23 years of age, and all but 1 were ambulatory. Vital capacity ranged from 47% to 70% predicted, and 1 patient needed nocturnal bi-level positive airway pressure. Limb flexor/extensor muscles and upper and lower extremities were affected equally. Pronounced neck flexor weakness was noted. Conclusions: Congenital myopathy caused by ACTA1 mutations is fatal in infancy in most cases. This study shows that the prevalence of a-actin myopathy in older patients with congenital myopathy is not negligible and that phenotypes can be quite mild.